OBJECTIVE:
To
assess
the
possibility
of
a
postfertilization
effect
in
regard
to
the
most
common
types
of
hormonal
emergency
contraception
(EC)
used
in
the
US
and
to
explore
the
ethical
impact
of
this
possibility.
DATA
SOURCES
AND
STUDY
SELECTION:
A
MEDLINE
search
(1966-November
2001)
was
done
to
identify
all
pertinent
English-language
journal
articles.
A
review
of
reference
sections
of
the
major
review
articles
was
performed
to
identify
additional
articles.
Search
terms
included
emergency
contraception,
postcoital
contraception,
postfertilization
effect,
Yuzpe
regimen,
levonorgestrel,
mechanism
of
action,
Plan
B.
DATA
SYNTHESIS:
The
2
most
common
types
of
hormonal
EC
used
in
the
US
are
the
Yuzpe
regimen
(high-dose
ethinyl
estradiol
with
high-dose
levonorgestrel)
and
Plan
B
(high-dose
levonorgestrel
alone).
Although
both
methods
sometimes
stop
ovulation,
they
may
also
act
by
reducing
the
probability
of
implantation,
due
to
their
adverse
effect
on
the
endometrium
(a
postfertilization
effect).
The
available
evidence
for
a
postfertilization
effect
is
moderately
strong,
whether
hormonal
EC
is
used
in
the
preovulatory,
ovulatory,
or
postovulatory
phase
of
the
menstrual
cycle.
CONCLUSIONS:
Based
on
the
present
theoretical
and
empirical
evidence,
both
the
Yuzpe
regimen
and
Plan
B
likely
act
at
times
by
causing
a
postfertilization
effect,
regardless
of
when
in
the
menstrual
cycle
they
are
used.
These
findings
have
potential
implications
in
such
areas
as
informed
consent,
emergency
department
protocols,
and
conscience
clauses.